Aqueous blends of colloidally dispersed polymers

ABSTRACT

The invention pertains to aqueous blends of colloidally dispersed polymers for use in making organic coatings which are hard and ductile at ambient temperature, which coatings remain stiff and elastic at temperatures well above their film-formation or drying temperature. In particular, the invention relates to specific combinations or thermoplastic blends of polymers of very high molecular weights. Such blends produce smooth, essentially crack-free coatings when dried conventionally under atmospheric pressure. Such blends are capable of developing the desired balance of properties without conventional amounts of volatile organic coalescing aids and without the need for chemical cure.

This application is a 371 of PCT/US96/12553 filed July 1996, thisapplication also claims the benefit of U.S. Provisional Application No.60/001,808 filed Aug. 4, 1995.

FIELD OF THE INVENTION

The invention pertains to aqueous blends of colloidally dispersedpolymers for use in making organic coatings which are hard and ductileat ambient temperature, and which remain stiff and elastic attemperatures well above their film-formation or drying temperature. Inparticular, the invention relates to blends of high-molecular-weight,thermoplastic polymers which are capable of developing these mechanicalproperties without conventional amounts of volatile organic coalescingaids and without the need for chemical cure.

BACKGROUND OF THE INVENTION

The performance of many coatings such as paints are governed by themechanical properties of one or more organic polymers which serve eitheras the coating per se or as a binder for other components of thecoating, such as pigments and fillers. For use in automotive paints, itis desirable that such polymers be hard at ambient temperature, asillustrated, for example, by a Knoop hardness number (KHN) greater thanabout 5 MPa (L. Dillinger, "Hardness Testing", LECO Corp., 3000 LakeviewAve., St. Joseph, Mich.; and ASTM D 1474-68). It is also desirable thatsuch polymers retain a certain degree of stiffness and elasticity at usetemperatures of 60° C. or higher, for example, exhibit a Young's modulus(E) greater than 10 MPa Amorphous polymers exhibit such properties onlywhen their glass transition temperature T_(g) is equal to or greaterthan the uppermost use temperature. The present invention relates to anew class of coating formulations to achieve these objectives.

Coatings and films are commonly characterized as either brittle orductile depending upon the manner in which they fail under tensile loads(I. M. Ward, Mechanical Properties of Solid Polymers, Chap. 12, JohnWiley & Sons, London, 1971). Brittle failure occurs at relatively smallstrains, for example≦20%, following a monotonic increase in the load. Bycontrast, ductile failure occurs at greater elongations, following apeak in the load/extension curve which is indicative of necking. Highlycross-linked, thermosetting polymer resins are generally brittle, oftenwith elongations<10%, whereas high-molecular-weight, linearthermoplastic polymers typically display a change in failure mode withtemperature. At temperatures much below T_(g) most thermoplastics arebrittle, but they undergo a transition from brittle to ductile failureas the temperature is increased, and the temperature of this transitiongenerally increases with increasing strain rate.

Ductility (especially elongations>10%) is a desirable property forcoatings on flexible substrates and also for coatings, such asautomotive paints, on metals, because ductility contributes to theability of the coating to survive impacts which dent or bend thesubstrate without causing cracking or peeling. The present inventionprovides a means to prepare coatings with a good balance of hardness,ductility, and stiffness, from very high-molecular-weight polymers,without the need for conventionally high amounts of volatile organiccomponents and without the need for cure chemistry.

Aqueous colloidal dispersions of polymers are increasingly important inthe paint industry because the coating constituents can be obtained inrelatively concentrated form (>20%), at moderate viscosities, and withlittle or no need for volatile organic solvents which constituteundesirable side-products in paint applications. However, the drying ofsuch dispersions to form uniform, crack-free coatings are subject tocertain well-known limitations. Such dispersions have beencharacterized, in each case, by a minimum film formation temperature,MFT, which is typically a few degrees below the glass transitiontemperature T_(g) of the colloidal-polymer particles (See, for example,G. Allyn, Film Forming Compositions, R. R. Myers & J. S. Long, Ed.,Marcel Dekker, N.Y., 1967). To whatever extent a polymer in a dispersionmay be plasticized by other components of the dispersion, the MFT may bereduced accordingly. If a dispersion is dried at a temperature (T) lessthan the MFT, a multitude of microscopic cracks, so-called "mud-cracks",which destroy the integrity of the coating, tend to develop late in thedrying process.

During drying, the actual temperature of an aqueous dispersion may belimited, by evaporative cooling, to a value much less than thetemperature of the surrounding atmosphere. Thus, regardless of oventemperature, coating temperatures typically do not exceed about 35° C.under atmospheric pressure, until substantially all of the water hasbeen lost (F. Dobler et al., J. Coil. Poly. Sci., 152, 12 (1992)). Thismeans that dispersions with MFT>35° C. are not generally useful forcoating applications. But polymers with unplasticized MFT≦35° C.generally do not provide adequate mechanical properties, includinghardness at higher temperatures of use.

Two strategies have most commonly been employed to bridge this gapbetween requirements for film formation and requirements for hardcoatings with elevated temperatures of use. First, volatile organicplasticizers (often described as coalescing aids or film formers) havebeen added to the dispersion. These dissolve in the polymer and lowerits T_(g) during drying, but ultimately volatilize at a later stage ofdrying, leaving the final resin at a higher T_(g). This strategy,however, conflicts with economic and environmental motivations to limitthe amount of volatile organic content (VOC's) in coating formulations.

A second strategy has been to formulate the dispersion with alow-molecular-weight thermosetting resin which, prior to cure, hassufficiently low T_(g) to provide film formation. After drying, curingat elevated temperatures, which result in cross-linking and chainextension reactions, raise the T_(g) and establish the ultimatelydesired mechanical properties.

In recent years, it has been found that coatings prepared from blends offilm-forming and non-film-forming aqueous dispersions of polymercolloids can be prepared with little or no need of a coalescing aid.Friel (EP 0 466 409 A1, Apr. 7, 1991) has shown that dispersion blendsof a "soft emulsion polymer" with T_(g) <20° C., at 20 to 60% by weight,in combination with a second "hard emulsion polymer" with T_(g) >20° C.exhibit MFT's≦9.35° C., without the need for a coalescing aid. All citedexamples, however, exhibited hardnesses of KHN≦2.7 MPa.

Snyder (U.S. Pat. No. 5,344,675, Sep. 6, 1994; U.S. Pat. No. 5,308,890,May 3, 1994) has shown that blends of a film-forming dispersion of a"multi-stage" latex polymer and a second non-film-forming dispersion canbe used to form coatings without the need for a coalescing aid. Snyderspecifies that each latex particle in the "multi-stage" component mustcontain between 50 and 95% by weight of a polymer with T_(g) <50° C. anda second polymer of higher T_(g). A certain balance was achieved betweencoating hardness, impact resistance and flexibility. The '890 patentalso states at column 3, lines 25-30, that "a comparable balance ofthese properties cannot be obtained by the use of other types ofsystems, such as, for example, a random copolymer, simple blends ofconventional emulsion polymers, a single type of multi-stage polymer,and the like." Among the examples cited for coatings made without acoalescing aid, three have a KHN>5.5 MPa, but these are characterized bya reverse impact resistance<2 inch-pounds and a flexibilitycorresponding to mandrel flexibility of 1/2". (According to ASTM D1737-62, a mandrel bend of 1/2" is approximately equivalent to a tensileelongation of 6.8%). Further examples are cited with a KHN between 4.0and 5.5 MPa, but with an impact resistances ranging from 4 to 60inch-pounds and a mandrel flexibility of 1/2" to 3/16".

BRIEF DESCRIPTION OF THE INVENTION

The invention pertains to an aqueous dispersion comprising a blend ofpolymer components each in the form of colloidal particles havingaverage hydrodynamic diameters less than about 1000 nm and preferablyless than about 200 nm, said polymer components comprising:

a first polymer component comprising about 20% to about 50% by volume ofthe total polymeric content and exhibiting a measured T_(g) (I) ofgreater than or equal to 49° C.;

a second polymer component comprising about 45% to about 80% by volumeof the total polymeric content and exhibiting a measured T_(g) (II) lessthan 49° C. and greater than 24° C.; and

a third polymer component comprising 0% to about 35% by volume of thetotal polymeric content and exhibiting a measured T_(g) (III) less than24° C.;

the sum of all three polymer components being 100% by volume;

wherein said first, second, and third polymer components each have aM_(w) greater than about 80,000 Daltons and are mutually adherent; andwherein the aqueous dispersion has a volatile organic content (VOC) ofless than about 20% by weight of the total polymeric content.

The invention further pertains to an aqueous dispersion which, upondrying at atmospheric pressure at temperatures greater than or equal to35° C. and annealing at temperatures greater than T_(g) (I), acontinuous, homogeneous coating is formed, which coating ischaracterized by a balance of hardness, ductility and stiffness attemperatures above T_(g) (II), which properties are represented,respectively, by a KHN≧about 3 MPa at 24° C., preferably by KHN≧5 MPa at24° C., tensile elongations greater than or equal to about 20%, andretained storage modulus, E' (1 Hz)>about 10 MPa at T=[T_(g) (I)+T_(g)(II)]/2; and wherein said properties are achievable without requiring,during drying or annealing, the cross-linking or branching of themolecular chains of said polymeric components to sensibly increase themolecular weights of said polymeric components.

In addition to polymer, the dispersion blends of the present inventionmay contain other constituents, including pigments, salts, surfactants,and UV stabilizers or inhibitors.

The invention further pertains to a clearcoat or colorcoat compositioncomprising about 10 weight % to about 50 weight % of polymeric bindersolids, said binder solids comprising about 30 weight% to about 100weight % of the aqueous dispersion described above. Such coatingcompositions, when dried, are capable of forming dense, crack-free filmsfor use on automotive and other substrates.

DETAILS OF THE INVENTION

Dispersion blends of the present invention have utility in producinghard organic coatings such as paints. For such applications, thedispersion blend may be mixed with other functional components such aspigments, fillers, or reagents for rheology modification, etc., as willbe understood by the skilled artisan. Such additional materials mayeither enhance or compromise certain properties of the final coating. Itshall, therefore, be understood that those physical propertiesexemplified by, and claimed for, coatings derived from the polymerdispersion blends of the present invention, containing essentially noother dispersed materials or solids, represent a starting point fromwhich the inclusion of other material may result in further improvementor mitigation, depending on the total properties of the finalcomposition.

The dispersion blends claimed in this invention form dense, essentiallycrack-free, hard, ductile organic coatings when dried at atmosphericpressure and temperatures≧about 40° C. and subsequently annealed attemperatures greater than the highest T_(g), namely T_(g) (I). Saidcoatings remain stiff and elastic at temperatures well above thefilm-forming or drying temperature without a requirement for cure, whichis to say without any chemical bond-forming reactions to increase M_(w)or cross-link the polymers.

An example of the combination of properties which can be achieved from abinary blend according to the present invention, is disclosed in Example44 (blend 50) below. A Type I polymer with T_(g) (I)=90° C. was blendedwith a Type II polymer of T_(g) (II)=34° C., resulting in a Knoophardness number (KHN) of 12 MPa, a Young's modulus (E) of 1.7 GPa, atensile elongation (e_(max)) of 46%, an impact resistance of 50inch-pounds (0.434 kg-m, 4.26 joule), a mandrel flexibility<1/8" (0.32cm), and at a temperature of 62° C. (midway between the two T_(g) 's), aretained storage modulus (E') of 0.31 GPa.

The present blends, depending on the particular embodiment, may or maynot include multistage polymer latex particles. Such particles arepredominantly amorphous, and dispersions of such particles are mostcommonly prepared directly by free-radical, emulsion polymerization, inwater, of unsaturated monomers such as acrylic acid (AA), methacrylicacid (MAA) and their respective esters or amides, including but notlimited to butyl methacrylate (BMA), butyl acrylate (BA), ethyl acrylate(EA), 2-methoxyethyl acrylate (MeOEA), 2-ethyl hexyl methylacrylate(EHMA) and methyl methacrylate (MMA), acrylonitrile, vinyl or vinylidenehalides, vinyl acetate, vinylpyridine, N-vinylpyrrolidone, styrene(Sty), 2-propenoic acid, 2-methyl,2-(2-oxo-l-imidazolidone) ethyl ester,etc.; but may also be prepared by dispersing, in water, polymers whichhave been first polymerized neat or in solution by condensationreactions or by addition reactions other than those initiated by freeradicals. See J. C. Padget, J. Coatings Techn., 66, p. 89 (1994) and D.C. Blackley, Emulsion Polymerization, Applied Science Publ. Ltd., London1975. In order that the dispersions of the invention be stable withrespect to sedimentation and/or flocculation, the colloidal particlesare typically stabilized by some combination of ionic functional groupson the polymer surface and/or surfactants adsorbed on their surface,and/or by low ionic strength of the aqueous phase.

The dispersion blends of this invention are further characterized by thefact that the different polymers in the blend remain phase separatedfollowing drying and annealing, at temperatures above the highest glasstemperature T_(g) (I), such that the resulting material exhibits two (ormore) glass temperatures, for example, with respect to itsthermo-mechanical properties (N. G. McCrum, B. E. Read, & G. Williams,Anelastic and Dielectric Effects in Polymeric Solids, Dover Publ., N.Y.,1991).

The blends of this invention are further distinguished by thedevelopment, during annealing, of mechanically strong interfaces betweenthe distinct polymer phases making them "mutually adherent." By"mutually adherent," with respect to polymer components of a dispersionblend, is meant that, after lamination and annealing of films made fromthe polymeric components, it is not possible to peel or separate thefilms along their original interface.

As illustrated in the examples, the three types of polymers I, II, andIII described herein serve different functions in the invention in termsof their film-forming abilities and their effects on the mechanicalproperties of a coating made therefrom. Colloidal dispersions of Type IIand/or III polymers alone are capable of forming dense, crack-freecoatings on drying at temperatures≧40° C. in the absence of anycoalescing aid. Dispersions of Type I alone cannot form such coatingswithout addition of some plasticizer as a coalescing aid, because theirMFT is otherwise too high. Types I or II can provide coatings which arehard (KHN>3) at ambient temperature (24° C.), because their T_(g)exceeds this temperature. However, in blends among the three types ofdispersions, it was found that that those for which the polymer weightcomprises≦50% of Type I can form dense, essentially crack-free film inthe absence of, or with less than conventional amounts of, one or moreorganic coalescing aids or agents. Conventional amounts of coalescingagents are typically about 25% by weight of total polymeric content,resulting in a relatively higher VOC (Volatile Organic Content). Incontrast, the present invention comprises less than about 20% VOC,preferably less than 10% VOC, and most preferably less than 5% VOC, asmeasured by heating a coating or other composition to 105° C. for 20minutes and determining the weight of material that is volatilized. SeeEPA (U.S. Environmental Protection Agency) Reference Method 24 and ASTMD-3960.

In blends according to the present invention, the ratio of Type II toType III polymers may be further adjusted to obtain desired mechanicalproperties of the final coating. For example, as illustrated in Example49 below, when the polymer weight comprises<40% Type III, the coatingwill exhibit a KHN≧about 3 MPa.

The T_(g) 's of the components of the blends may be achieved with orwithout the addition of a non-volatile plasticizing agent to thosepolymers whose intrinsic T_(g) is higher than specified. Accordingly,the relevant T_(g) 's of the components of a mixture are the resultingT_(g) 's as measured by a DSC of the mixture.

Type I polymers have the highest T_(g). This determines the maximumtemperature at which the coating may exhibit a certain degree ofstiffness and elasticity, for example a storage modulus E'>0.01 GPa, ata frequency of 1 Hz. The exact magnitude of E' depends upon the weightfraction of the Type I polymer, such that higher fractions provide ahigher E'. As illustrated by Example 44 (B-50) below and Table 8, ablend containing 50% of a Type I polymer may exhibit a value of E' attemperatures between T_(g) (I) and T_(g) (II) very close to the maximumvalue theoretically attainable from an isotropic blend of the purecomponents (Z. Hashin & S. Shtrikmann, J. Mech. Phys. Sol, 11, 127(1963)).

The coatings are preferably annealed at a temperature well above thehighest T_(g), mamely T_(g) (I), in order to obtain optimum mechanicalproperties. In the examples described below, annealing was for 20minutes at 130° C. Without annealing, the dried coatings prepared fromdispersion blends of the invention were found to be too brittle, ascharacterized by elongations<10% and no necking under tension. Theeffects of annealing are thought to involve some combination of thefollowing processes: (1) secondary coalescence of the Type I particles,involving growth of mutual interfaces and diffusion of chains acrossthose interfaces, (2) relaxation of elastic stresses within the Type IIphase domains and increasing inter diffusion in these domains whichcomprise a continuous network, and (3) a limited degree of interdiffusion between Type I and Type II phase domains which strengthensthese heterogeneous interfaces. (See, for example, S. Voyutsky,Autohesion and Adhesion of High Polymers, Wiley-Interscience, N.Y.,1963)

An important aspect of this invention is the discovery that theductility of the coatings derived from dispersion blends dependscritically upon the interfaces between the different polymer phasedomains. Examples in Tables 6, 7 and 10 show that films prepared fromdispersion blends containing types I, II, and III, in proportionsdescribed by the invention, show good ductility. For example blends ofP(MMA/BA) Type I with P(MMA/EA) Type II in Table 6 exhibit necking andhigh elongations characteristic of a tough, ductile material. Table 10shows similar results for blends of P(MMA/BMA) Type I with P(BMA) TypeII.

For the purposes of this invention, the mutual adherence between any twopolymers, for example of Types I and II, may be evaluated according tothe following test. Independent films, with thicknesses greater thanabout 20 μm, of each polymer are prepared by a method such as drying ofthe polymer dispersion, casting a film from solution, or compressionmolding a film from a dried polymer powder. Specimens of each film arethen laminated together, under pressure (e.g., 100 MPa), at atemperature of at least 40° C. above the higher T_(g), represented byT_(g) (I), for a period of at least 20 minutes, so as to create an areaof intimate molecular contact. This area can be any convenient size,e.g., 2 cm by 10 cm. The laminated specimen is then allowed to cool toambient temperature (e.g., 24° C.) and an attempt is made to separatethe two components by peeling along the original interface.

When the interfacial strength in such a laminate is less than thecohesive fracture strength of either polymer tested, e.g., Type I, TypeII or Type III, then it is possible to cleanly peel or separate the twocomponents, which is to say the laminate fails adhesively.Alternatively, if the mutual adhesive strength is comparable to thecohesive strength of either component then it is no longer possible tomechanically peel or separate the polymer films along their originalinterface. Instead, the sample will typically fail cohesively byfracturing or tearing through the thickness of one or both components.Cohesive and adhesive strengths may be quantitatively characterized bythe critical energy release rate, G, as described in Fracture Mechanicsof Polymers, by J. G. Williams, Ellis and Horwood, Ltd., West Sussex,England, 1984. However, for present purposes, the simple qualitativedistinction between cohesive failure and adhesive failure of theselaminates is sufficient to determine whether such a pair is mutuallyadherent or non-adherent. Thus, mutual adherence between a given pair ofpolymers, measured in this way, is a reliable indicator of the ductilityof coatings and films which may be prepared from drying and annealing ofaqueous colloidal dispersions of the same two polymers, as disclosed inthis invention.

In particular, when an aqueous dispersion of colloidal polymers of TypeI and Type II (or II and III, or I and III), containing less than about20% , preferably less than 10%, most preferably less than 5%, volatileorganic content by weight of total polymeric content, is dried andannealed at a temperature at least 40° C. higher than the highest T_(g)for a period of at least 20 minutes, the resulting film may exhibit, at24° C., a tensile failure which is either brittle (e.g., withelongations less than 10% with no significant yielding) or ductile(e.g., with elongations greater than 10%, accompanied by yielding ornecking). As illustrated by examples in Tables 7 and 10, ductile failureis observed in every case where the polymer pairs are mutually adherent,and brittle failure is observed when they are not mutually adherent.Similiarly, Example 55 may be characterized as marginally adherent sincethe laminates fail by a combination of adherent and cohesive modes. Thecorresponding blends (Examples 67-70) exhibit tensile failures rangingfrom brittle to ductile, depending upon the blend composition.

Polymer-polymer compatibility plays an important role in blends of thisinvention. Coatings fabricated from the dispersion blends of theinvention remain chemically heterogeneous, each component polymerremaining in different phase domains as can be distinguished by suchmethods as electron microscopy and by various manifestations of multipleglass transition temperatures, for example, in dynamic mechanicalmeasurements. This heterogeneity may be the result of true immiscibilityof the component polymers in the thermodynamic sense of equilibriumphase separation. Or it may be that the polymers are actuallythermodynamically miscible under the processing conditions but, onaccount of their high molecular weights, they remain phase segregatedfor kinetic reasons. Thus, for M_(w) ≧80,000 daltons, it would takeextremely long times for diffusion to achieve complete mixing of amutually compatible pair. However, it may be noted that for very highM_(w), the vast majority of polymer pairs, even copolymers which differin the proportion of comonomers, are, in fact, thermodynamicallyimmiscible.

Pairs of acrylic polymers which exhibit a strong interface (asexemplified by cohesive failure of laminates and formation of ductileblends) often contain a common comonomer. It may be that this commonstructural element imparts a limited degree of thermodynamiccompatibility, for example, similar solubility coefficients for the twocopolymers, such that a limited degree of inter diffusion may occurwhich strengthens the interface. Examples in Tables 6, 7 and 10 belowillustrate the correlation of ductility with the presence of a commoncomonomer in both components of a binary blend. In Table 6 below, thecommon comonomer is methyl methacrylate, and in Table 10, it is butylmethacrylate. Note that for 50/50 blends in Table 10, only marginalductility is obtained when the common comonomer comprises only 25% ofthe Type I component.

Coating properties obtained from the dispersion blends of the invention,especially the balance of properties, and most especially thecombination of ductility with KHN>5 MPa, represent substantialimprovements over the prior art as disclosed by the examples of Friel,in EP 0 466 409 A1, Apr. 7, 1991, and of Snyder, in U.S. Pat. Nos.5,344,675; 5,308,890, referred to above. Moreover, this balance ofproperties is especially unobvious in that they can be obtained fromsimple emulsion polymers, not only multi-stage polymers, incontradiction to Snyder's teaching.

The aqueous colloidal copolymer dispersions of the present invention canbe made in various ways known to those skilled in the art. Although notwishing to be limited to the following methods, all dispersions in theexamples below were made by standard batch emulsion polymerization.using sodium dodecylsuflate (SDS, 0.1 to 1.0 mole percent based onmonomer) or other material as identified below as surfactant, andammonium persulfate (APS) initiator. Polymerizations were run tocompletion under monomer-starved conditions at around 33% solids.

EXAMPLES

The general procedure for producing the polymers employed in thisinvention is as follows. All monomers, initiators, and surfactantsincluding SDS, dioctyl sulfosuccinate (DOSS), and the ammonium salt ofnonylphenol ethoxylate sulfate (Ipegal® CO-425), are commerciallyavailable (Aldrich Chemical Co., Milwaukee, Wis.) and were used asreceived.

A 2-L resin kettle (4-L for the 800 g reactions) equipped with acondenser, addition funnel, mechanical stirrer, and temperaturecontroller probe was charged with the water required to produce 33 wt %solids, less 100 ml, and SDS. The contents were stirred and heated to80° C. until all the SDS dispersed. The APS was dissolved in 100 mlwater, and 80 ml of this solution was added to the kettle. All of themonomers except the MAA (if used) were mixed and divided into two equalportions. One portion of the monomers was charged to the additionfunnel, and about 20 ml was added to the kettle. The remainder was addeddropwise over about 1/2 hour, keeping the temperature in the kettlebetween 80 and 85° C. The MAA (if used in the particular Example) wasmixed with the second half of monomer, which was charged to the additionfunnel and added slowly over 1 hour, keeping the temperature in thekettle between 80 and 85° C. After the addition, the remainingpersulfate solution was added, and the latex heated for 1/2 hour at 85°C. The latex was then heated to boiling until no more monomer appearedin the condenser. The latex was then cooled and filtered through a finepaint strainer.

The resulting dispersions were stable, cloudy, with Brookfieldviscosities ranging from 5 to 10 poise (0.5-1.0 Pasec). A 10 g latexsample was poured into a 5 cm round aluminum pan which was then placedin a 75° C. vacuum oven at about 400 mm Hg vacuum overnight. Solidscontent, differential scanning calorinetry (DSC), and gel permeationchromatography (GPC) measurements were made on this dried material, asdescribed below.

The T_(g) values reported are mid-point temperatures in degrees Celsiusfrom DSC scans recorded according to ASTM D3418-82. Temperaturedependence of the mechanical properties was characterized by DMA,performed on a commercially available instrument (Model DMA-7®,Perkin-Elmer, Norwalk, Conn.). Specimens of free-standing film (e.g.,0.06×4×10 mm) were mounted between parallel clamps at a static tensionof 20 mN, and subjected to sinusoidal dynamic stress of 10 mN amplitudeat a frequency of 1.0 Hz. The storage modulus, E', was measured as thesample was heated from -20° C. to 90° C. at 5° C./min.

Molecular weights were measured by GPC. The equipment employed consistedof the following. Columns: 2 pl gel 5 μm mixed c, 300 mm×7.5 mm (PolymerLabs, Amherst, Mass., part# 1110.6500); Detector: Waters 410®refractive-index detector (Waters, Inc., Milford, Mass.); Pump: Waters590® (Waters, Inc., Milford, Mass.); and Column Heater (Waters, Inc.,Milford, Mass.).

The refractive-index detector internal temperature was 30° C.; solvent,tetrahydroflran (THF), 0.025% butylated hydroxytoluene (BHT) inhibited(Omnisolv); Flow rate, 1 ml/min; Concentration, 0.1% (10 mg(10 ml).Samples were prepared by dissolving overnight with gentle shaking, andthen filtering through 0.5 μm filter (Millipore, Bedford, Mass.).

Hydrodynamic diameters (particle size) of the polymeric particles weredetermined by quasielastic light scattering in the range from about 50to 150 nm, using a Brookhaven Instruments BI-90® instrument (BrookhavenInstruments, Brookhaven, N.Y.). See generally Paint and SurfaceCoatings: Theory and Practice, ed. by R. Lambourne, Ellis Horwood Ltd.,West Sussex, England, 1987, pp. 296-299, and The Application of LaserLight Scattering to the Study of Biological Motion, ed. by J. C.Earnshaw and M. W. Steer, Plenum Press, N.Y., 1983, pp. 53-76.

Coatings were prepared by casting or spraying the dispersion onto flatsubstrates (glass or metal), drying in a temperature-controlled oven atatmospheric pressure (generally at 80° C.), followed by annealing at ahigher temperature above T_(g) (I) (generally 130° C.). For sprayapplications, an anti-foaming agent such as2,3,7,9-tetramethyl-5-decyne4,7-diol (Surfynol-104®, Air Products andChemicals, Inc., Allentown, Pa.) was added to the dispersion at lessthan 2% of solids. This had no detectable plasticizing or film-formationeffect. Film formation was evaluated after drying and after annealing.In particular, the formation of micro-cracks which penetrate the entirethickness of the coating ("mud-cracks") was noted as unacceptable filmformation.

Hardness measurements were made on coatings 0.001 to 0.003" (0.00254 to0.00762 cm) thick on glass substrates at temperatures between 21° C. and24° C. at ambient by means of a commercially available microindentationinstrument (LECO Corp., St. Joseph, Mich., part number M-400-G1).Free-standing films were prepared from coatings cast on glass plates.

The dispersions of these copolymers were generally evaluated fromdraw-downs (0.005 to 0.015 inches, 0.0127 to 0.0381 cm) on glass, withsubsequent drying in air at 70° C. for 10 minutes, and annealing at 130°C. for 20 minutes. Final coating thickness was about 0.001 to 0.0025inches (0.00254 to 0.00635 cm). All the film thicknesses were measuredwith a micrometer. This protocol closely resembles typical drying andcure cycles for thermoset coatings.

The mechanical properties of binary blends were evaluated at ambienttemperature and humidity (e.g., 23° C., 50% relative humidity or RH)both for free-standing films (0.0025", 0.00635 cm, thick) and forcoatings (0.001", 0.00254 cm, thick) applied on primed steel panels(cold rolled steel with C168 conversion and ED5000 primer, ACTLaboratories, Troy, Mich.). All samples were first dried at 80° C. for 5minutes and annealed at 130° C. for 20 minutes.

Tensile testing ((Instron, Canton, Mass., part number MTAOPR66) wasperformed on film specimens 50 to 100 μm thick (0.002 to 0.004 inches),6.25 mm (0.25 inches) wide with 2.5 cm (1 inch) gauge lengths, at astrain rate of 0.017/sec at temperatures between 22° C. and 24° C., andat a cross-head speed of 2.5 cm/minute (1 in/min). Impact tests wereperformed with a drop tower equipped with 1.56 cm (0.625 in) die and1.25 cm (0.5 in) hemispherical indenter (ASTM D2794). Impact performancewas comparable regardless of whether the coated surface was on the sameor opposite side of the impact. Mandrel bends were performed with aconical mandrel (Gardner, Pompano Beach, Fla., MN-CM/ASTM, ASTM D522)representing diameters from 3.13 to 3.75 cm (1/8 to 1.5 in).

EXAMPLES 1-37

Examples 1-37 illustrate the synthesis of the different types ofcopolymers for use in blends of the present invention. The generalmethod as previously described was followed. Tables 1, 2 and 3 belowreport the results of representative latex procedures. In the tables,"Size" refers to the grams of monomer used; "Soap" is the moles ofsurfactant (SDS unless otherwise noted) per mole of monomer, presumingthe molecular weight is 100; APS is in grams; the proportions of monomerare in weight %; and M_(n) and M_(w) are in thousands.

                                      TABLE 1                                     __________________________________________________________________________    (Type 1 Copolymers)                                                                      APS                   Part.   Mn  Mw                                 Ex. No. Size.sup.†  Soap.sup.‡ (g) MMA BMA EA BA Sty                                                   MAA Size nm Tg° C.                                                     × 10.sup.-3 ×                                                     10.sup.-3                        __________________________________________________________________________     1  200                                                                              0.0070                                                                            0.4                                                                              74.0   25.0     1.0    71  150 517                                 2 200 0.0053 0.4 98.0     2.0  114  191 467                                   3 400 0.0042 1.0 98.0     2.0  124  303 728                                   4 400 0.0042 1.0 98.0     2.0  118  130 603                                   5 200 0.0070 0.2 78.0  20.0   2.0  80 194 628                                 6 200 0.0053 0.4 98.0     2.0  124  131 399                                   7 200 0.0070 0.4 83.0   15.0  2.0  90 185 555                                 8 200 0.0094 0.4 84.0   15.0  1.0  90 152 428                                 9 200 0.0070 0.4 85.0   15.0   57.0 82 169 475                               10 400 0.0052 0.4 85.0   15.0    81 216 698                                   11 400 0.0042 0.4 84.0   15.0  1.0 70.0 89 223 676                            12 800 0.0042 0.4 84.0   15.0  1.0 73.0 90 418 940                             13* 200 0.0025 0.4 84.0   15.0  1.0 91.0 100  234 891                        14 800 0.0042 0.4 84.0   15.0  1.0  86 334 852                                15 200 0.0070 0.4 50.0 50.0      69 267 1100                                  16 200 0.0035 0.4 75.0 25.0      98 186 536                                   17 200 0.0018 0.4 64.0   15.0 20.0 1.0  83 192 608                            17-1 200 0.0018 0.4 99.0     1.0 84.0 66 155 414                            __________________________________________________________________________     *Soap is Ipegal ® CO425                                                   .sup.† Size = g. of monomer used                                       .sup.‡ Soap = moles surfactant/mole monomer                   

                                      TABLE 2                                     __________________________________________________________________________    (Type 2 Copolymers)                                                                      APS                     Part Size                                                                          Tg Mn  Mw                               Ex. No. Size.sup.†  Soap.sup.‡ g MMA BMA EA MeOEA Sty                                                    MMA nm ° C. ×                                                    10.sup.-3 × 10.sup.-3    __________________________________________________________________________    18  200                                                                              0.0070                                                                            0.4                                                                              58.0   15.0                                                                             25.0   2.0      42 159 838                              19 200 0.0053 0.4 56.0  15.0 25.0  4.0  42 159 750                            20 200 0.0053 0.4 58.0  15.0 25.0  2.0  40 193 929                            21 200 0.0042 0.4 58.0  40.0   2.0  49 232 833                                22 200 0.0042 0.4 48.0  50.0   2.0  34 178 855                                23 200 0.0042 0.4 50.0  50.0    57.0 30 303 1200                              24 400 0.0042 0.4 50.0  50.0     30 221 1110                                  25 400 0.0042 0.4 49.0  50.0   1.0 73.0 36 268 1100                           26 800 0.0042 0.4 49.0  50.0   1.0 76.0 33 402 1530                            27* 200 0.0025 0.4 49.0  50.0   1.0 75.0 33 242 1090                         28 200 0.0021 0.4 49.0  50.0   1.0 71.0 33 253 992                            29 200 0.0021 0.4 49.0  50.0   1.0 70.0 34 299 1090                            30** 200 0.0021 1.0 49.0  50.0   1.0 74.0 34 178 802                         31 200 0.0070 0.4  100.0     54.0 30 375 1360                                 32 800 0.0042 0.4 49.0  50.0   1.0  32 432 1390                               33 200 0.0018 0.4 46.0  50.0   4.0  35 217 869                                34 200 0.0018 0.4 29.0  50.0  20.0 1.0                                        34-1 200 0.0018 0.4 74.0  25.0    1.0 95.0 29 136 344                       __________________________________________________________________________     *Soap is Ipegal CO425                                                         **Soap is DOSS                                                                .sup.† Size = g. of monomer used                                       .sup.‡ Soap = moles surfactant/mole monomer                   

                                      TABLE 3                                     __________________________________________________________________________    (Type 3 Copolymers)                                                                      APS                     Tg Mn  Mw                                    Ex. No. Size.sup.†  Soap.sup.‡ g MMA EHMA EA MeOEA BA                                               MAA ° C. ×                                                       10.sup.-3 × 10.sup.-3         __________________________________________________________________________    35  200                                                                              0.0042                                                                            0.4                                                                              24.0    50.0                                                                             25.0   1.0                                                                              -1  84  297                                  36 200 0.0094 0.4 22.0    77.0 1.0 -24  233 1090                              37 200 0.0094 0.3  100.0     -5 445 1410                                    __________________________________________________________________________     .sup.† Size = g. of monomer used                                       .sup.‡ Soap = moles surfactant/mole monomer                   

EXAMPLE 38

This Example illustrates the blending of copolymers and the effects ofblending on film formation in the absence of plasticizers. The followingcomponents were mixed in a test tube with vigorous stirring: 1.0 mlP(MMA/EA/MeOEA/MAA) (Example 18 from Table 2, T_(g) 42° C.), 0.10 ml ofphenyltrumethylarmonium hydroxide, (PTMAOH), (0.42 molar in deionizedwater), and 1.0 ml of P(MMA/EA/MAA) (Example 1 from Table 1, T_(g) 71°C.). The resulting dispersion was fluid, moderately viscous and stableover 20 minutes with no evidence of flocculation. A coating was drawnonto a glass microscope slide (2"×3", 5.01 to 7.162 cm) by means of adoctor blade (clearance 0.015", 0.0381 cm) and then dried in an oven at130° C. at atmospheric pressure for 20 minutes. The resulting coatingappeared optically clear with no cracks and no evidence of exudedsurfactant. The coated surface was hydrophobic and homogeneous ascharacterized by advancing and receding contact angles of 43° and 30°respectively. The hardness was KHN=10.4 MPa.

EXAMPLES 39-46

These Examples illustrate binary blends of a Type I polymer with Type IIor III polymers. In order to determine the maximum fraction of Type Ipolymer in blends which could be dry without plasticizer into crack-freecoatings, blends similar to Example 38 were prepared. Films were castand dried as in Example 38. All samples were dried at 80° C./5 minutesfollowed by drying at 130° C. for 20 minutes. In those examples withpH>6, methacrylic acid residues on the polymer were neutralized witheither phenyltrimethyl ammonium hydroxide (Aldrich Chemical Co.,Milwaukee, Wis.) or triethanolamine (Aldrich Chemical Co., Milwaukee,Wis.). Table 4 below indicates the ranges of film forming compositionand hardnesses for various binary dispersion blends, with compositionsbased on weight % solids.

As shown in Table 4, all the binary and ternary blends containing morethat 55% of Type I polymer were found unsuitable for film formation inthe absence of added plasticizers due to crack formation during drying.(Comparative Examples are indicated "Comp." in Table 4.) This supportsthe theory that if the percentage of high T_(g) (Type I) colloidparticles is too high, such that the MFT remains above 35° C. in theabsence of added plasticizer, then attempts to create a coating bydrying under atmospheric pressure results in the formation of cracks andfissures which destroy the integrity of the coaing. It is believed thatthese cracks are a consequence of internal capillary stresses whichdevelop when the drying water front recedes into a porous coating. It ismoreover believed that these pores are a direct consequence of theinability of the polymer particles to deform into space-filing shapesduring drying. Apparently, by including a suitable fraction of low T_(g)polymer particles (Type II or III) in the dispersion, these particlescan deform sufficiently to fill the pores, thereby preventing theformation of internal capillary stresses and cracks. Apparently, theminimum quantity of deformable particles required to fill the pores isabout 45%. Also, in the binary blends of Example 41, the Type IIcomponent (the polymer of Example 21) has a T_(g) of 49° C., which isabout borderline for Type I polymers. Example 41 shows that, in thisExample, at least 70% of the Type II (Example 21) polymer was requiredto avoid cracking in binary blends with the polymer Example 2.Apparently, for this particularly stiff Type II polymer, a higherfraction thereof is required to fill the pores.

A preferred example of the invention for binary blends is Example 7(Type I), 20 to 50% by weight, blended with Example 22, 80-45% byweight.

                  TABLE 4                                                         ______________________________________                                                           Type II         KHN                                          Ex. No. Type I (Tg), % or III (Tg), % pH MPa Comments                       ______________________________________                                        39     Ex. 1 (71° C.)                                                                     Ex. 18 (42° C.)                                       A (Comp.) 59 41 7.0 12.9 cracks                                               B 52 48 7.5 12.9 no cracks                                                    C 48 52 7.5 12.5 "                                                            40 Ex. 2 (114° C.) Ex. 18 (42° C.)                              A 50 50 7 15.3 no cracks                                                      B 40 60 7 18.3 "                                                              C 30 70 7 12.2 "                                                              D 20 80 7 11.1 "                                                              41 Ex. 2 (114° C.) Ex. 21 (49° C.)                              A (Comp.) 50 50 7 17.6 cracks                                                 B (Comp.) 45 55 7 15.6 "                                                      C (Comp.) 40 60 7 15.3 "                                                      D (Comp.) 35 65 7 15.1 "                                                      E 30 70 7 13.9 no cracks                                                      42 Ex. 2 (114° C.) Ex. 22 (34° C.)                              A 50 50 7 15.0 no cracks                                                      B 45 55 7 14.2 "                                                              C 40 60 7 13.2 "                                                              D 35 65 7 13.2 "                                                              E 30 70 7 11.2 "                                                              G 25 75 7 10.9 "                                                              H 20 80 7 10.1 "                                                              43 Ex. 2 (114° C.) Ex. 35 (-1° C.)                              A (Comp.) 60 40 -- 6.6 cracks                                                 B 50 50 -- 4.3 no cracks                                                      C 40 60 -- 2.4 "                                                              D 30 70 -- 0.7 "                                                              E 20 80 -- 0.7 "                                                              44 Ex. 7 (90° C.) Ex. 22 (34° C.)                               A (Comp.) 60 40 6 -- cracks                                                   B 55 45 6 12.1 no cracks                                                      C 50 50 6 12.0 "                                                              D 45 55 6 11.3 "                                                              E 40 60 6 10.8 "                                                              F 35 65 6 10.2 "                                                              G 30 70 6 9.5 "                                                               H 25 75 6 9.2 "                                                               I 20 80 6 8.6 "                                                               45* Ex. 12 (90° C.) Ex. 26 (34° C.)                             A 23.6 55.0 8 10 no cracks                                                    B 19.4 45.3 8 12 "                                                            46 Ex. 17 Ex. 34                                                              A (Comp.) 60 40  11.2 cracks                                                  B 50 50  11.2 no cracks                                                       C 40 60  10.0 "                                                               D 30 70  9.3 "                                                                E 20 80  7.7 "                                                                  Ex. 34-1                                                                    46-1 Ex. 17-1 (66° C.) (29° C.)                                 A 50 50 -- 8.8 no cracks                                                      B 40 60 -- 7.4 no cracks                                                      C 30 70 -- 5.9 no cracks                                                      D 20 80 -- 4.8 no cracks                                                    ______________________________________                                         *Indicates samples containing white TiO.sub.2 pigment (TiPure ® R902      at 6 and 11% PVC).                                                            "Comp." indicates a Comparative Example.                                 

EXAMPLES 47 TO 49

Examples 47-49 illustrate ternary blends between Type I, Type II, andType III polymer (acrylic) latex dispersions, with no plasticizer. Theexamples, summarized in Table 5, were made by the same procedure asExample 38, except that the prescribed proportion of Type III polymerwas also added. The compositions were dried at 80° C./5 minutes followedby drying at 130° C. for 20 minutes. The data illustrate variations inhardness with composition for coatings prepared without plasticizers.Again, comparative examples, indicated by "Comp." in Table 5, show thatblends containing more than 55% of Type I polymer exhibited cracks.

Preferred examples of the invention for ternary blends are Example 9(Type I)≦50% by weight blended with Example 23 (Type II), 25 to 69%, andExample 38 (Type III), 7 to 35% by weight. Note these have KHN≧5 MPa.

                                      TABLE 5                                     __________________________________________________________________________    Ex. No.                                                                            Type I (Tg), %                                                                       Type II (Tg), %                                                                       Type III (Tg), %                                                                      pH                                                                              KHN MPa                                                                            Comments                                   __________________________________________________________________________    47   Ex. 2 (114° C.)                                                               Ex. 20 (40° C.)                                                                Ex. 35 (-1° C.)                                      A (Comp.) 70 15 15 7 -- cracks                                                B (Comp.) 60 20 20 7 -- "                                                     C 50 25 25 7 7.8 no cracks                                                    D 40 30 30 7 7.1 "                                                            E 30 35 35 7 5.2 "                                                            F 20 40 40 7 3.3 "                                                            48 Ex. 2 (114° C.) Ex. 21 (149° C.) Ex. 35 (-1°                                           C.)                                          A 50 25 25 7 8.6 "                                                            B 45 27.5 27.5 7 6.8 "                                                        C 40 30 30 7 7.1 "                                                            D 35 32.5 32.5 7 4.9 "                                                        E 30 35 35 7 5.0 "                                                            49 Ex. 9 (82° C.) Ex. 23 (30° C.) Ex. 36 (-24° C.)       A 50 25 25 6 6.6 "                                                            B 40 30 30 6 5.7 "                                                            C 30 35 35 6 4.6 "                                                            D 20 40 40 6 3.1 "                                                            E 50 37.5 12.5 6 9.4 "                                                        F 40 45 15 6 8.3 "                                                            G 30 52.5 17.5 6 6.0 "                                                        H 20 60 20 6 4.7 "                                                            I 50 42.8 7.2 6 10.2  "                                                       J 40 51.4 8.6 6 9.5 "                                                         K 30 60 10 6 7.9 "                                                            L 20 68.6 11.4 6 5.5 "                                                      __________________________________________________________________________

EXAMPLES 50-62

These Examples 50-62 illustrate correlations between mutual adherenceand blend ductility, involving a comparison of failure modes for blendsand corresponding laminates.

Table 6 summarizes the results of laminate-adhesion tests for variouspairs of acrylic copolymers and mechanical properties of films preparedfrom a 50:50 blend of the corresponding dispersions. ComparativeExamples, which did not fail cohesively, are indicated by "(C)" in Table6. Blend films are characterized as ductile if the elongation at breakexceeds 10%. Laminate failure is characterized as adhesive if the twofilms can be cleanly pealed apart without tearing, and cohesive if oneor the other component tears before they can be peeled apart. Note thatthe distinction between ductile and brittle blends is independent ofhardness (KHN). Ductility is strongly correlated with mutual adherence,i.e., blends which are ductile correspond to laminates which failcohesively. It is likewise consistent that the laminates for Example 55fail by a combination of cohesive and adhesive modes and thecorresponding blends display elongations ranging from 8.5% to 97%depending upon blend composition (see Table 7).

                  TABLE 6                                                         ______________________________________                                                          Laminate                                                                             Blend                                                Ex. No.                                                                              Type I  Type II  Type III                                                                            Failure                                                                              KHN  failure                             ______________________________________                                        50(C)  --      Ex. 30/31                                                                              --    adhesive                                                                             3    brittle                               51(C) Ex. 12 Ex. 31 -- " 6.2 "                                                52(C) Ex. 9  Ex. 31 -- -- 7.0 "                                               53(C) Ex. 12 -- Ex. 37 " 3.5 "                                                54 Ex. 15 -- Ex. 37 -- 2.8 (marginal)                                         55 Ex. 16 Ex. 31 -- adhesive/ --  (marginal)                                      cohesive                                                                  56 Ex. 16 Ex. 26 -- cohesive 12 ductile                                       57 Ex. 15 Ex. 31 -- -- 7 "                                                    58 Ex. 15 Ex. 33 -- -- 11.6 "                                                 59 Ex. 15 Ex. 31 -- -- 5.2 "                                                  60 Ex. 15 Ex. 32 -- -- 8.0 "                                                  61 Ex. 15 -- Ex. 36 -- 2.4 "                                                  62 Ex. 12 -- Ex. 36 -- 1.9 "                                                ______________________________________                                    

EXAMPLES 63-70

These Examples 63 to 70 illustrate the mechanical properties of binaryblends in which butyl methacrylate is a common comonomer. Table 7summarizes hardness and tensile properties for binary blends ofpoly(butyl methacrylate), a Type II homopolymer (Example 31) with twodifferent Type I co-polymers prepared from butyl methacrylate and methylmethacrylate. The blends with Ex 15 are apparently more ductile (asreflected by greater elongation at break) than those with Example 16.This appears to correlate with increasing content of common comonomer(butyl methacrylate) in the Type I components, namely 25% in Example 16versus 50% in Example 15.

The examples of Table 7 show that, for blends with poly(butylmethacrylate) as the Type II component, the ductility can be enhanced byincreasing the content of butyl methacrylate in the Type I component.Comparative Example 63, labelled "(C)" in Table 7, represents a limitingcase of marginal ductility in that the sample necks under tension butnevertheless fails at less than 10% elongation.

The mutual adherence between interfaces of immiscible polymers, whichcorrelates with ductility of the blend, is believed to relate to theextent of molecular intermixing at the interface. Apparently, when twopolymers are more nearly related in their thermodynamic properties, asfor example, when they share a significant fraction of common comonomer,then such intermixing is enhanced.

                                      TABLE 7                                     __________________________________________________________________________                    KHN                                                                              Modulus                                                                            necking                                                                             tenacity                                                                          elongation                                  Ex. No.                                                                           Type 1                                                                              Type 2                                                                              MPa                                                                              GPA  %  MPA                                                                              MPA %                                           __________________________________________________________________________        Ex. 16 Wt %                                                                         Ex. 31 Wt %                                                           63(C) 50 50 6.8 1.4   5 32 28 8.5                                             64 40 60 5.3 0.99 7 23 17 21                                                  65 30 70 3.9 0.88 7 18 10 35                                                  66 20 80 2.5 0.81 6 16 14 97                                                   Ex. 15 Wt % Ex. 31 Wt %                                                      67 50 50 6.3 1.2    6.5 26 16 45                                              68 40 60 4.4 1.0  7 21 15 73                                                  69 30 70 3.8 0.81 6 18 16 127                                                 70 20 80 3.4 0.66   6.5 15 13 131                                           __________________________________________________________________________

EXAMPLE 71

This Example illustrates, based on the blends of Example 44. the tensiletesting of bay blends. The mechanical properties of blends (Example 44)between the Type I polymer (Example 12) and the Type II polymer (Example26) were compared with those of the pure components. (Films of purepolymer of Example 26 were prepared with the aid of a volatileplasticizer. All others were prepared by drying and annealing of thecorresponding dispersions without added plasticizer.) Table 8 summarizestensile, impact, and flexibility at ambient temperature (about 24° C.).Films of the pure Type I polymer are brittle, as exemplified by anelongation of 5% without yielding, while films of all the blends from 50to 20% Type I polymer (44C, 44E, 44G, and 44I) were ductile(elongations>10% following yielding). This ductility is also manifest inthe resistance to impact and mandrel bends. The values of Young'smodulus (E) are typical of thermoplastic polymers at T<T_(g) and isessentially independent of the blend composition. The yield stress(σ_(y)) increases with the content of Type I polymer. The compositionsand hardness of the binary blends are given in Table 4 above. E isYoung's modulus, σ_(y) represents the stress maximum due to neckingwhich occurs at elongations of about 5%. All coatings with the exceptionof Example 12 were cast from dispersions without plasticizer.

                                      TABLE 8                                     __________________________________________________________________________                E  σ.sub.v                                                                           Tenacity                                                                           Impact                                            Example No. % Type I GPa MPa Elongation % MPa inch-lbs Mandrel              __________________________________________________________________________    12     100  1.5                                                                              n.a                                                                               5     52   --  --                                            44C 50 1.7 38  46 29 50 <1/8"                                                 44E 40 1.8 34 107 27 -- --                                                    44G 30 1.7 31 165 27 80 <1/8"                                                 44I 20 1.6 28 187 27 --                                                       26  0 1.0 26 294 26 --  --                                                  __________________________________________________________________________

EXAMPLE 72

This Example illustrates, based on the blends of Examples 44 and 48, thedynamic mechanical properties of coatings obtained from binary andternary blends. Table 9 summarizes the dynamic storage modulus E' at afrequency of 1 Hz at 24° C. and 62° C. (The latter temperaturecorresponds to the mid-point between T_(g) (I) and T_(g) (II)). At 24°C., E' is nearly independent of blend composition because both Type Iand II polymers remain glassy at this temperature. For comparison,theoretical maximum and minimum values of E' (62° C.) were calculatedfrom the values for the corresponding pure components at the sametemperature according to the equations of Z. Hashin & S. Shtrikmann (J.Mech. Phys. Sol., 1963, vol 11, pp 127-140). This theory describes theminimum and maximum moduli which can be achieved from all possibleisotropic structures composed of the same two component phases at agiven volume fraction. For Example 4C, the experimental value of E' (62°C.) turns out to be 79% of the theoretical maximum and 79 times greaterthan the minimum. For Example 4I, E' (62° C.) is only 6% of thetheoretical maximum and 5.6 times greater than the minimum. Suchvariations suggest that the Type I phase comprises a more extended orcontinuous structural element in E 44C than in E 44I.

Table 10 summarizes dynamic mechanical data for ternary blends ofExample 8. Storage moduli for the series of ternary blends in Example48, where the weight fractions of Type II and Type III components weremaintained equal throughout, have also been exemplified in Table 10. Inthis series, similar to the binary blends, the value of E' at 81.5° C.(the midpoint between T_(g) (I) and T_(g) (II)) remains greater than 10MPa. The value at ambient temperatures is slightly reduced relative tothe binary blends due to the presence of Type III component with T_(g)(III)<24° C. At 24° C., E' decreases with increasing content of Type IIIpolymer because T_(g) (III)=-1° C. However, E' (81.5° C.)>10 MPa inT-30, comparable to values for binary blends with the same content ofType I polymer (see, for example, Table 9).

                                      TABLE 9                                     __________________________________________________________________________                       E' (24° C.)                                                                  E' (62° C.)                                                                  Theory (62° C.)*                        Ex. No.                                                                           % Type I                                                                           T.sub.σ (I) ° C.                                                      T.sub.σ (II) ° C.                                                     GPa   GPa   min max (GPa)                                  __________________________________________________________________________    7   100  90   --   2.2   1.4   --  --                                           44C 50 90 34 1.9 0.31 0.0039 0.52                                             44E 40 90 34 1.9 0.14 0.0030 0.40                                             44G 30 90 34 1.8 0.038 0.0023 0.29                                            44I 20 90 34 1.8 0.010 0.0018 0.18                                            22  0 -- 34 1.4 0.0011 -- --                                                __________________________________________________________________________

                                      TABLE 10                                    __________________________________________________________________________                              E' (24° C.)                                    Ex. No. % Type I T.sub.σ (I) ° C. T.sub.σ (II)                                           ° C. T.sub.σ (III) °                                      C. GPa E' (81.5° C.)                   __________________________________________________________________________    48A  50   114  49   -1    1.1   0.29                                            48B 45 114 49 -1 1.05 0.20                                                    48C 40 114 49 -1 0.74 0.099                                                   48D 35 114 49 -1 0.59 0.047                                                   48E 30 114 49 -1 0.54 0.019                                                 __________________________________________________________________________

What is claimed is:
 1. An aqueous dispersion comprising a blend ofpolymer components each in the form of colloidal particles havingaverage hydrodynamic radii less than 500 nm, said polymer componentscomprising:a first polymer component comprising 20% to 50% by volume ofthe total polymeric content and exhibiting a measured T_(g) (I) ofgreater than or equal to 49° C.; a second polymer component comprising45% to 80% by volume of the total polymeric content and exhibiting ameasured T_(g) (II) less than 49° C. and greater than 24° C.; and athird polymer component comprising 0% to 35% by volume of the totalpolymeric content and exhibiting a measured T_(g) (III) less than 24°C.; wherein each of said first, second, and third polymer components hasa M_(w) greater than 80,000 Daltons and are mutually adherent; andwherein the aqueous dispersion has a volatile organic content of lessthan 20% by weight of the total polymeric content.
 2. The aqueousdispersion as recited in claim 1 wherein said particles have averagehydrodynamic radii less than 100 nm.
 3. The aqueous dispersion asrecited in claim 1, wherein the measured T_(g) 's of said componentsreflect the effect of the addition of a non-volatile plasticizing agent.4. The aqueous dispersion as recited in claim 1 wherein said volatileorganic content is less than 10% by weight of the total polymericcontent of said aqueous dispersion.
 5. The aqueous dispersion as recitedin claim 1, wherein, upon drying at atmospheric pressure at temperaturesgreater than or equal to 35° C. and annealing at temperatures greaterthan T_(g) (I), a continuous, homogeneous coating is formed which ischaracterized by a balance of hardness, ductility and stiffness attemperatures above-T_(g) (II), said properties represented,respectively, by KHN≧3 MPa at 24° C., tensile elongations greater thanor equal to 20%, and E' (1 Hz)>10 MPa at T=[T_(g) (I)+T_(g) (II)]/2; andwherein said properties are achieved without, cross-linking or branchingof the molecular chains of said polymeric components, during drying orannealing, such as to sensibly increase the molecular weights of saidpolymeric components.
 6. The aqueous dispersion as recited in claim 5wherein the hardness of said film is represented by KHN≧5 MPa.
 7. Theaqueous dispersion as recited in claim 1, 2, 3, 4 or 5 wherein saidpolymeric components are homopolymers or copolymers comprisingcomonomers selected from the group consisting of acrylic and methacrylicacid and the respective esters and amides thereof, acrylonitrile,styrene and its derivatives, 1,3-butadiene, isoprene, ethylene,propylene, chloroprene, vinyl acetate, vinyl choride, vinyl fluoride,and vinylidene fluoride.
 8. The aqueous dispersion as recited in claim 7wherein said polymeric components are linear or branched copolymers. 9.A paint or coating composition comprising about 10 weight % to about 50weight % of polymeric binder solids, said binder solids comprised ofabout 30 weight % to about 100 weight % of the aqueous dispersion asrecited in claim 1 or 5.